Method for controlling an engine with VGT and EGR systems

ABSTRACT

A method for controlling an internal combustion engine is provided. The engine includes a variable geometry turbocharger (VGT) system and an exhaust gas recirculation (EGR) system. In a boost mode, the VGT system is controlled with a closed loop based on boost pressure. In an EGR mode, the VGT system is controlled with a closed loop based on EGR rate. Further, in the EGR mode, the EGR system is controlled with a closed loop based on boost pressure. Preferred control techniques are also provided including non-linear compensation and adaptive feed forward control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling an internalcombustion engine including a variable geometry turbocharger (VGT)system and an exhaust gas recirculation (EGR) system.

2. Background Art

In the control of internal combustion engines, the conventional practiceutilizes an engine controller with inputs, outputs, and a processor thatexecutes instructions to control the engine including its varioussystems. The engine may include a variable geometry turbocharger (VGT)system and an exhaust gas recirculation (EGR) system. U.S. Pat. No.6,305,167 describes an existing method of controlling an engine.

The engine business is quite competitive. Increasing demands are beingplaced on manufacturers to provide improved performance, reliability,and durability while meeting increasing emissions requirements. For theforegoing reasons, there is a need for an improved method forcontrolling an engine.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide animproved method for controlling an engine with VGT and EGR systems.

In carrying out the object, a method for controlling an internalcombustion engine is provided. The engine includes an engine blockdefining a plurality of cylinders, a controller, a variable geometryturbocharger (VGT) system and an exhaust gas recirculation (EGR) system.The VGT system provides pressurized intake air to the plurality ofcylinders. The EGR system provides a metered portion of the exhaustgases to the plurality of cylinders. The controller communicates withthe VGT system and the EGR system to control the engine. The methodcomprises selecting an engine operating mode from a plurality of modesincluding a boost mode and an EGR mode. When the selected engineoperating mode is the boost mode, the VGT system is controlled with aclosed loop based on a desired boost pressure and a measured boostpressure such that the measured boost pressure tracks the desired boostpressure. When the selected engine operating mode is the EGR mode, theVGT system is controlled with a closed loop based on a desired EGR rateand a measured EGR rate such that the measured EGR rate tracks thedesired EGR rate. Further, in the EGR mode, the EGR system is controlledwith a closed loop based on a desired boost pressure and a measuredboost pressure such that the measured boost pressure tracks the desiredboost pressure.

In a preferred embodiment, when the selected engine operating mode isthe boost mode, controlling the VGT system with the closed loop furthercomprises comparing the desired boost pressure to the measured boostpressure to determine an error signal. The error signal is processed todetermine a commanded VGT position. An adaptive feed forward VGTposition map is utilized to determine a feed forward VGT position. TheVGT system is controlled based on the commanded VGT position and thefeed forward VGT position. More preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded VGT position based on thecompensated error signal.

Further, in the preferred embodiment, when the selected engine operatingmode is the EGR mode, controlling the VGT system with the closed loopfurther comprises comparing the desired EGR rate to the measured EGRrate to determine an error signal. The error signal is processed todetermine a commanded VGT position. An adaptive feed forward VGTposition map is utilized to determine a feed forward VGT position. TheVGT system is controlled based on the commanded VGT position and thefeed forward VGT position. More preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded VGT position based on thecompensated error signal.

Further, in the preferred embodiment, when the selected engine operatingmode is the EGR mode, controlling the EGR system with the closed loopfurther comprises comparing the desired boost pressure to the measuredboost pressure to determine an error signal. The error signal isprocessed to determine a commanded EGR position. A feed forward EGRposition map is utilized to determine a feed forward EGR position. TheEGR system is controlled based on the commanded EGR position and thefeed forward EGR position. More preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded EGR position based on thecompensated error signal.

It is appreciated that although methods of the present inventioncomprise controlling the VGT system with a closed loop when boost modeis selected, and controlling the VGT system and the EGR system withclosed loops when EGR mode is selected, certain special engineconditions during boost mode and/or EGR mode may require alternativecontrol techniques during these special instances without departing fromthe scope of the present invention. For example, in the preferredembodiment, controlling the EGR system further comprises controlling theEGR system based solely on the feed forward EGR position when the feedforward EGR position is a full open position or a full closed position.For all other feed forward EGR positions aside from the full openposition and the full closed position, in the preferred embodiment,closed loop control based on boost pressure is still used. Further,methods of the present invention are suitable for many different enginetypes.

Further, in carrying out the present invention, an internal combustionengine is provided. The engine includes an engine block defining aplurality of cylinders, a controller, a variable geometry turbocharger(VGT) system and an exhaust gas recirculation (EGR) system. The VGTsystem provides pressurized intake air to the plurality of cylinders.The EGR system provides a metered portion of the exhaust gases to theplurality of cylinders. The controller communicates with the VGT systemand the EGR system to control the engine. The controller is programmedto control the internal combustion engine by selecting an engineoperating mode from a plurality of modes including a boost mode and anEGR mode. When the selected engine operating mode is the boost mode, theVGT system is controlled with a closed loop based on a desired boostpressure and measured boost pressure such that the measured boostpressure tracks the desired boost pressure. When the selected engineoperating mode is the EGR mode, the VGT system is controlled with aclosed loop based on a desired EGR rate and a measured EGR rate suchthat the measured EGR rate tracks the desired EGR rate. Further, whenthe selected engine operating mode is the EGR mode, the EGR system iscontrolled with a closed loop based on a desired boost pressure and ameasured boost pressure such that the measured boost pressure tracks thedesired boost pressure.

In a preferred embodiment, when the selected engine operating mode isthe boost mode, controlling the VGT system with the closed loop furthercomprises comparing the desired boost pressure to the measured boostpressure to determine an error signal. The error signal is processed todetermine a commanded VGT position. An adaptive feed forward VGTposition map is utilized to determine a feed forward VGT position. TheVGT system is controlled based on the commanded VGT position and thefeed forward VGT position. More preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded VGT position based on thecompensated error signal.

Further, in the preferred embodiment, when the selected engine operatingmode is the EGR mode, controlling the VGT system with the closed loopfurther comprises comparing the desired EGR rate to the measured EGRrate to determine an error signal. The error signal is processed todetermine a commanded VGT position. An adaptive feed forward VGTposition map is utilized to determine a feed forward VGT position. TheVGT system is controlled based on the commanded VGT position and thefeed forward VGT position more preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded VGT position based on thecompensated error signal.

Further, in the preferred embodiment, when the selected engine operatingmode is the EGR mode, controlling the EGR system with the closed loopfurther comprises comparing the desired boost pressure to the measuredboost pressure to determine an error signal. The error signal isprocessed to determine a commanded EGR position. A feed forward EGRposition map is utilized to determine a feed forward EGR position. TheEGR system is controlled based on the commanded EGR position and thefeed forward EGR position. More preferably, processing the error signalfurther comprises utilizing a non-linear compensation map to determine acompensated error signal based on the error signal. A linear controlleris utilized to determine the commanded EGR position based on thecompensated error signal.

Further, in the preferred embodiment, controlling the EGR system furthercomprises controlling the EGR system based solely on the feed forwardEGR position when the feed forward EGR position is a full open positionor a full closed position.

The above object and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the preferred embodiment when taken in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates an internal combustion engine withVGT and EGR systems in the preferred embodiment of the presentinvention;

FIG. 2 is a diagram that illustrates VGT system control in the boostmode;

FIG. 3 is a diagram that illustrates VGT system control in the EGR mode;and

FIG. 4 is a diagram that illustrates EGR system control in the EGR mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an internal combustion engine including an engineblock 10 defining a plurality of cylinders, with each cylinder receivingfuel from a fuel injector. In a preferred embodiment, the internalcombustion engine is a compression-ignition internal combustion engine,such as a heavy duty diesel fuel engine. The engine includes a VGTsystem for providing pressurized intake air to the plurality ofcylinders. VGT turbine 12, compressor 14, and cooler 16 compose the VGTsystem. The pressure of the engine exhaust gases causes VGT turbine 12to spin. VGT turbine 12 drives compressor 14. Compressor 14 pressurizesintake air to develop increased power during combustion. Charge aircooler 16 cools the pressurized air. The VGT system has moveablecomponents that can change the turbocharger geometry by changing thearea or areas in the turbine stage to which exhaust gases flow, and/orchanging the angle at which the exhaust gases enter or leave theturbine. The turbocharger supplies varying amounts of turbo boostpressure depending on the turbocharger geometry. The VGT system inembodiments of the present invention may take any suitable form. Forexample, a variable inlet nozzle to the turbine, a moveable sidewall inthe turbine housing, or any other controllable air pressurizing deviceincluding the above examples, and including a modulated wastegate valvemay compose the VGT system.

EGR valve 18 and cooler 20 compose the EGR system. The EGR systemintroduces a metered portion of the exhaust gases into the intakemanifold. The exhaust gases lower combustion temperatures to reduce thelevel of oxides of nitrogen (NO_(x)) that are produced. In embodimentsof the present invention, the EGR system may take any suitable form. Forexample, a butterfly valve is a suitable EGR valve.

With continuing reference to FIG. 1, the engine also includes acontroller 22. Controller 22 communicates with the VGT system and theEGR system to control the engine. Controller 22 may take any suitableform. A suitable controller includes a programmed microprocessor. Inoperation, controller 22 receives signals from the various vehiclesensors and executes programmed logic embedded in hardware and/orsoftware to control the engine.

FIGS. 2–4 illustrate VGT system and EGR system control in the preferredembodiment. Generally, the VGT system provides pressurized intake air tothe engine cylinders, and the EGR system provides a metered portion ofthe exhaust gases to the engine cylinders. The turbo boost pressureresults in increased power while the introduction of exhaust gaseslowers combustion temperatures. Controller 22 operates the engine andcontrols the VGT system and EGR system in accordance with the currentengine operating mode which is based on any number of engine conditions.The plurality of available engine operating modes includes a boost modeand an EGR mode. FIG. 2 illustrates VGT system control in the boostmode.

A desired boost pressure is determined based on engine speed anddemanded torque at desired boost pressure map 30. Boost sensor 32determines a measured boost pressure. Summer 34 compares the desiredboost pressure to the measured boost pressure to determine an errorsignal. A non-linear compensation map 36 determines a compensated errorsignal based on the input error signal. A linear controller such asproportional/integral/derivative controller 38 determines a commandedVGT position based on the compensated error signal. An adaptive feedforward VGT position map 40 determines a feed forward VGT position basedon engine speed and torque. Summer 42 controls the VGT system based onthe commanded VGT position from PID controller 38 and the feed forwardVGT position from adaptive feed forward VGT position map 40. The closedloop VGT system control causes the measured boost pressure from boostsensor 32 to track the desired boost pressure from desired boostpressure map 30. VGT system control shown in FIG. 2 is used in the boostmode, when the EGR valve is fully closed. VGT system control when theEGR valve is fully open or partially open is shown in FIG. 3. EGR systemcontrol is shown in FIG. 4.

With continuing reference to FIG. 2, the purpose of the feed forward VGTposition is to give a close approximation of what state the VGT shouldbe in to achieve the target boost. Initially, the feed forward map iscalibrated with values that will achieve the target boost at eachspecific engine speed and torque. The adapting feature of the feedforward logic is used to compensate for turbo-to-turbo andengine-to-engine variability. While the engine is operating inpseudo-steady state, values in the feed forward table are updated basedon actual controller output values.

Because the VGT system is a non-linear system that will responddifferently depending on engine speed and torque, non-linearcompensation logic 36 determines a compensated error signal. Thenon-linear compensation map maps a boost pressure error to a VGTposition error. Specifically, the map receives a boost pressure error asinput and divides the input value by a table value representing thefirst derivative of boost pressure with respect to VGT position command.The table is indexed by engine speed and torque. One suitable techniqueto populate the table is to run an engine at steady state for all enginespeed and torque combinations, and slew the VGT position command over areasonable range and record the change in boost pressure.

FIG. 3 illustrates VGT system control in the EGR mode. The VGT system iscontrolled with a closed loop based on the desired EGR rate and themeasured EGR rate such that the measured EGR rate tracks the desired EGRrate. The desired EGR rate is determined from a desired EGR rate map 50based on engine speed and torque. The measured EGR rate is determined byEGR flow sensor 52. Summer 54 compares the desired EGR rate from map 50to the measured EGR rate from EGR flow sensor 52 to determine an errorsignal. A non-linear compensation map 56 is utilized to determine acompensated error signal based on the error signal from summer 54. Alinear controller such as proportional/integral/derivative controller 58determines the commanded VGT position based on the compensated errorsignal. An adaptive feed forward VGT position map 60 is utilized todetermine a feed forward position based on engine speed and torque.Summer 62 provides a signal to control the VGT system based on thecommanded VGT position from PID 58 and the feed forward VGT positionfrom adaptive feed forward VGT position map 60.

Similar techniques as those described previously with respect to FIG. 2are utilized to update table values for adaptive feed forward VGTposition map 60 and determine table values for non-linear compensationmap 56. While the engine is operating in pseudo-steady state, values inthe feed forward table are updated based on actual controller outputvalues. The non-linear compensation map 56 maps EGR flow rate error toVGT position error. By running an engine at steady state for all enginespeed and torque combinations and slewing VGT position command over areasonable range and then recording changes in EGR flow rate, the tablemay be calibrated.

FIG. 4 illustrates EGR system control in the EGR mode. The EGR system iscontrolled with a closed loop based on a desired boost pressure and ameasured boost pressure such that the measured boost pressure tracks thedesired boost pressure. Desired boost pressure is determined as afunction of values from desired boost maps 68 and 70. The desired boostmay be taken from one table or the other depending on engine conditions,or may be a weighted average of values from both tables. Summer 74compares desired boost pressure to measured boost pressure from boostpressure sensor 72. Non-linear compensation map 75 is calibrated withvalues that map boost error to EGR valve position error. This map may becalibrated by running the engine at steady state and slewing EGRposition command through a reasonable range, at recording boost changes.The output of non-linear compensation map 75 is a compensated errorsignal and a linear controller such as proportional/integral/derivativecontroller 76 determines the commanded EGR position based on thecompensated error signal. A feed forward EGR position map 80 determinesa feed forward EGR position. Map 80 optionally may be adaptive. The EGRsystem is controlled based on the command of the EGR position from PID76 and the feed forward EGR position from feed forward EGR position map80. To increase transient engine performance, a rapid transition fromclosed to open loop control over the EGR valve position may be used.Switch 78 selectively blocks the output of PID controller 76 when openloop control is desired. Examples of engine conditions where open loopEGR valve control would be used include when the EGR valve is commandedto fully closed or to fully open. Other positions for the EGR valvegenerally utilized closed loop EGR system control of FIG. 4 and closedloop VGT system controller of FIG. 3.

In operation of the engine, the control systems shown in FIGS. 2–4cooperate to control the VGT system and the EGR system. In the boostmode, the EGR valve is fully closed preferably by a direct command fromfeed forward EGR position map 80 with switch 78 blocking the output ofPID 76 as shown in FIG. 4. With the EGR valve fully closed, the VGTsystem is controlled with closed loop control around boost pressure asshown in FIG. 2, and turbocharger geometry is varied to control air flowthrough the turbine and achieve a desired boost pressure. In the EGRmode, FIG. 3 illustrates that the VGT system is controlled with closedloop based on EGR flow rate. Air flow through the VGT system iscontrolled such that the desired EGR flow rate is achieved. At the sametime, EGR valve position is controlled in closed loop fashion based onboost pressure as shown in FIG. 4.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

1. A method for controlling an internal combustion engine, the engineincluding an engine block defining a plurality of cylinders, acontroller, a variable geometry turbocharger (VGT) system and an exhaustgas recirculation (EGR) system, the VGT system providing pressurizedintake air to the plurality of cylinders and the EGR system providing ametered portion of the exhaust gases to the plurality of cylinders, thecontroller communicating with the VGT system and the EGR system tocontrol the engine, the method comprising: selecting an engine operatingmode from a plurality of modes including a boost mode and an EGR mode;when the selected engine operating mode is the boost mode, controllingthe VGT system with a closed loop based on a desired boost pressure anda measured boost pressure such that the measured boost pressure tracksthe desired boost pressure; and when the selected engine operating modeis the EGR mode, controlling the VGT system with a closed loop based ona desired EGR rate and a measured EGR rate such that the measured EGRrate tracks the desired EGR rate, and controlling the EGR system with aclosed loop based on a desired boost pressure and a measure boostpressure such that the measured boost pressure tracks the desired boostpressure.
 2. The method of claim 1 wherein when the selected engineoperating mode is the boost mode, controlling the VGT system with theclosed loop further comprises: comparing the desired boost pressure tothe measured boost pressure to determine an error signal; processing theerror signal to determine a commanded VGT position; utilizing anadaptive feed forward VGT position map to determine a feed forward VGTposition; and controlling the VGT system based on the commanded VGTposition and the feed forward VGT position.
 3. The method of claim 2wherein processing the error signal further comprises: utilizing anon-linear compensation map to determine a compensated error signalbased on the error signal; and utilizing a linear controller todetermine the commanded VGT position based on the compensated errorsignal.
 4. The method of claim 1 wherein when the selected engineoperating mode is the EGR mode, controlling the VGT system with theclosed loop further comprises: comparing the desired EGR rate to themeasured EGR rate to determine an error signal; processing the errorsignal to determine a commanded VGT position; utilizing an adaptive feedforward VGT position map to determine a feed forward VGT position; andcontrolling the VGT system based on the commanded VGT position and thefeed forward VGT position.
 5. The method of claim 4 wherein processingthe error signal further comprises: utilizing a non-linear compensationmap to determine a compensated error signal based on the error signal;and utilizing a linear controller to determine the commanded VGTposition based on the compensated error signal.
 6. The method of claim 1wherein when the selected engine operating mode is the EGR mode,controlling the EGR system with the closed loop further comprises:comparing the desired boost pressure to the measured boost pressure todetermine an error signal; processing the error signal to determine acommanded EGR position; utilizing a feed forward EGR position map todetermine a feed forward EGR position; and controlling the EGR systembased on the commanded EGR position and the feed forward EGR position.7. The method of claim 6 wherein processing the error signal furthercomprises: utilizing a non-linear compensation map to determine acompensated error signal based on the error signal; and utilizing alinear controller to determine the commanded EGR position based on thecompensated error signal.
 8. The method of claim 6 wherein controllingthe EGR system further comprises: controlling the EGR system basedsolely on the feed forward EGR position when the feed forward EGRposition is a full open position or a full closed position.
 9. Aninternal combustion engine, the engine including an engine blockdefining a plurality of cylinders, a controller, a variable geometryturbocharger (VGT) system and an exhaust gas recirculation (EGR) system,the VGT system providing pressurized intake air to the plurality ofcylinders and the EGR system providing a metered portion of the exhaustgases to the plurality of cylinders, the controller communicating withthe VGT system and the EGR system to control the engine, the controllerbeing programmed to control the internal combustion engine by: selectingan engine operating mode from a plurality of modes including a boostmode and an EGR mode; when the selected engine operating mode is theboost mode, controlling the VGT system with a closed loop based on adesired boost pressure and a measured boost pressure such that themeasured boost pressure tracks the desired boost pressure; and when theselected engine operating mode is the EGR mode, controlling the VGTsystem with a closed loop based on a desired EGR rate and a measured EGRrate such that the measured EGR rate tracks the desired EGR rate, andcontrolling the EGR system with a closed loop based on a desired boostpressure and a measure boost pressure such that the measured boostpressure tracks the desired boost pressure.
 10. The engine of claim 9wherein when the selected engine operating mode is the boost mode,controlling the VGT system with the closed loop further comprises:comparing the desired boost pressure to the measured boost pressure todetermine an error signal; processing the error signal to determine acommanded VGT position; utilizing an adaptive feed forward VGT positionmap to determine a feed forward VGT position; and controlling the VGTsystem based on the commanded VGT position and the feed forward VGTposition.
 11. The engine of claim 10 wherein processing the error signalfurther comprises: utilizing a non-linear compensation map to determinea compensated error signal based on the error signal; and utilizing alinear controller to determine the commanded VGT position based on thecompensated signal.
 12. The engine of claim 9 wherein when the selectedengine operating mode is the EGR mode, controlling the VGT system withthe closed loop further comprises: comparing the desired EGR rate to themeasured EGR rate to determine an error signal; processing the errorsignal to determine a commanded VGT position; utilizing an adaptive feedforward VGT position map to determine a feed forward VGT position; andcontrolling the VGT system based on the commanded VGT position and thefeed forward VGT position.
 13. The engine of claim 12 wherein processingthe error signal further comprises: utilizing a non-linear compensationmap to determine a compensated error signal based on the error signal;and utilizing a linear controller to determine the commanded VGTposition based on the compensated error signal.
 14. The engine of claim9 wherein when the selected engine operating mode is the EGR mode,controlling the EGR system with the closed loop further comprises:comparing the desired boost pressure to the measured boost pressure todetermine an error signal; processing the error signal to determine acommanded EGR position; utilizing a feed forward EGR position map todetermine a feed forward EGR position; and controlling the EGR systembased on the commanded EGR position and the feed forward EGR position.15. The engine of claim 14 wherein processing the error signal furthercomprises: utilizing a non-linear compensation map to determine acompensated error signal based on the error signal; and utilizing alinear controller to determine the commanded EGR position based on thecompensated error signal.
 16. The engine of claim 14 wherein controllingthe EGR system further comprises: controlling the EGR system basedsolely on the feed forward EGR position when the feed forward EGRposition is a full open position or a full closed position.